Explain how crumple zones and seat belts work together to reduce the risk of injury to passengers during a car collision.

Eduqas GCSE Physics — 4.3 Safety in public transport · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Crumple zones are designed to absorb impact energy by deforming, which increases the time (or distance) over which the car decelerates during a collision. A longer deceleration time reduces the force on the occupants, because force equals change in momentum divided by time. Seat belts keep passengers from continuing to move forward at the vehicle’s original speed once the car has stopped. They also stretch slightly, further increasing the deceleration time for the passenger and thereby reducing the force experienced.

Examiner tips

  • Use the exact phrase ‘increase the time over which the car decelerates’ to hit the first point.
  • Show the force equation (F=Δp/Δt) to justify the reduction in force.
  • Explain that seat belts both restrain motion and stretch to add deceleration time.
  • Link each point directly to injury reduction to satisfy the ‘explain’ command word.

Common mistakes

  • Confusing crumple zones with airbags – they are separate safety features.
  • Omitting the force equation or the role of seat‑belt stretch in reducing force.
  • Failing to mention that seat belts prevent the passenger from hitting the interior of the car.

Mark scheme (4 marks)

  1. Crumple zones increase the time (or distance) over which the car decelerates during a collision
  2. A longer deceleration time means the force experienced by passengers is reduced (since force = change in momentum / time)
  3. Seat belts prevent passengers from continuing to move forward (at the original speed) after the car has stopped
  4. Seat belts also stretch slightly, increasing the time over which the passenger decelerates, further reducing the force on the passenger

Key terms in this question

crumple zones · seat belts

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